Re the second diagram of this eBook Section; there is no reference in the text to the resistor which is included between the mechanical switch in the base bias circuit located between base and supply battery positive. What is this resistor's purpose, how should its value be ascertained and what would happen if it wasn't there ? (these questions should reveal just how limited my general electronics understanding is Hope someone can help.

dandeeny

 

Here
http://kaizerpowerelectronics.dk/calculators/transistor-base-resistor-calculator/
http://www.electronics-tutorials.ws/amplifier/transistor-biasing.html
Max.

 

Your answer appears in the first two lines of that same page.

Because a transistor's collector current is proportionally limited by its base current, it can be used as a sort of current-controlled switch. A relatively small flow of electrons sent through the base of the transistor has the ability to exert control over a much larger flow of electrons through the collector.

A relatively small flow of electrons (current). That is the purpose of the resistor. It is called biasing. Too large a flow would damage the transistor, so it is set and limited by the resistor.

To calculate the resistor note that
the voltage drop across the resistor = supply minus the base voltage.

Resistance required = this voltage divided by base current.

The base current is obviously the switched collector current divided by the transistor gain (usually 50 -100) for switching transistors.